I just want to clarify for perhaps non-horsey people reading this thread - the lethal gene in horses being talked about is linked to FRAME overo, specifically. Not other common overo patterns like splash or sabino. It is known as Overo Lethal White syndrome (OLWS) or Lethal White Overo (LWO), which isn't an entirely accurate name because it is the frame overo gene that is lethal.

(eta: it is lethal due to an abnormal and dysfunctioning colon, IIRC. There is no treatment or cure that I have heard of - foals must be PTS or die naturally. They appear healthy and normal otherwise. Interestingly, Paint breeders report a far fewer percentage of lethal white foals than the 25% it "should" be when breeding frame to frame. More like 4-5%, I've read in some cases.)

so you call black dogs "blue"? if its black pigmented, black nose and eyerims, black patches, its not a blue dog. its DD or Dd. blue is dd. a blue merle would be Mmdd. if its got black pigment why would you call it blue?

It's just what people call it. Just like red merles are technically liver.

I know in danes merle (grey with black splotches and black nose etc) is not considered the same as blue merle....(grey with darker grey splotches and blue leather)?

Slate merle is usually the term for a blue (dilute) merle. So the black in the coat is diluted to blue and then merled. 'Blue merle' is a dog who is black and not dilute and merle. A blue merle will have a black nose and a slate merle will have a blue nose <--- easiest way to tell.

Lilac/isabella is red/chocolate/liver that has been diluted. And that can be merled as well.